Trouba didn't do anything that went against league policy, as he handed in his no-trade list with Detroit on it, but fans, particularly in Detroit, were shocked to hear this considering Trouba is from Michigan, and many thought he would want to play back home, which clearly isn't the case.
Trouba had what many would describe as an okay year for the Rangers, scoring only 3 goals and 19 points, with a slightly subpar +/- rating of -4, very average numbers to say the least. Clearly, the Rangers had higher expectations of their captain, which could explain why they have been trying to move him recently.